1. Field of the Invention
The present invention relates to a circuit arrangement for centrally-controlled telecommunications exchange systems, particularly telephone exchange systems, comprising two parallel-operating central control units and two groups of sub-centralized switch devices, and comprising two bidirectional data bus lines respectively connecting a central control unit to the sub-centralized switch devices of a group. In addition, the arrangement comprises two bidirectional auxiliary data bus lines respectively connecting the sub-centralized switch devices of a respective group to the central control unit assigned to the other group of sub-centralized switch devices, and parallel operation is provided for both central control units in the data exchange with the sub-centralized switch devices of the group assigned thereto via the appertaining bidirectional data bus line. Further, alternate circuit operation is provided, given service interruption of a central control unit or of its assigned data bus line via the respective other central control unit to the sub-centralized sequential logic system of the group of the central control unit affected by the service interruption and bidirectional bus amplifiers looped into the auxiliary data bus lines whereof, respectively, two are connected into an auxiliary data bus line extending from the central control unit to the sub-centralized switch devices of the respective other group and whereof, respectively, a first is connected to the sub-centralized switch devices of the one group and a second is connected to the central control unit of the other group of sub-centralized switch devices.
2. Description of the Prior Art
A circuit arrangement of the type generally set forth above is set forth in the technical book "Rechnergesteuerte Vermittlungssysteme" by Peter R. Gerke, Springer Verlag, Berlin/Heidelberg/New York, 1972, Page 109. An alternate circuit mode in the manner described therein presumes that each of the two separate control units is connectible to every switch device of each of the two groups. For parallel operation to be carried out without error, the two mutually-independent data bus lines respectively assigned to a central control unit and its group of switch devices are required. The two additional, auxiliary data bus lines are required for the alternate circuit mode so that a respective central control unit can enter into communication with the switch devices of the group of switch devices assigned to the other (momentarily fault-affected) central control unit.
Given a parallel operation of central control units in the addressed manner, therefore, a respective central control unit cooperates with the switch devices of the group assigned thereto in a fault-free condition. A central control unit and the switch devices of the group assigned thereto are therefore likewise structurally combined such that they form a unit, in that, for example, they are accommodated in a cabinet rack. The switch devices being addressed can be a matter of dependent, sub-centralized control equipment, of sub-memories, of termination circuits of data transmission links and the like. Depending on the respective three-dimensional extent for which a data bus line extends from a central control unit to the switch devices of its group, a bus amplifier is required. Such bus amplifiers are usually bidirectional because a data transmission must be capable of being executed both from a central control unit to each of the switch devices and in the opposite direction. Primarily, however, such bus amplifiers are required for the alternate circuit mode. As already explained, it is thereby necessary that a central control unit can collaborate with the switch devices of the group assigned to the other central control unit. Naturally, the auxiliary data bus lines provided for this purpose have a greater through-dimensional length than the data bus lines and bus amplifiers and are therefore mainly employed in these auxiliary data bus lines.
The bus amplifiers not only have the job of amplification (and of equalization as well under given conditions) of the signals to be transmitted, but also have the job of coupling and decoupling. In the alternate circuit case, the undisturbed central control unit replacing the fault-affected central control unit must be able to collaborate with the switch devices of the group assigned to the fault-affected central control unit. The appertaining auxiliary data bus line for the alternate circuit mode must therefore be coupled to the undisturbed central control unit, particularly to its data bus line. Given the conclusion of the alternate circuit mode, this auxiliary data bus line must be correspondingly decoupled so that the fault-free parallel operation of both central control units can continue.
In addition to the above, however, there is also the other fault occurrence that a central control unit together with the switch devices of this group are affected by an outage of the operating voltage. Therefore, when a central control unit has a common voltage supply with the switch devices of its group, and this voltage supply fails, then it is not only this central control unit that goes off line but also the switch devices of the group assigned thereto are also down. In case of such a disturbance, therefore, an alternate circuit is superfluous because, in addition to the affected central control unit, the switch devices assigned thereto are also not operational. Such a fault occurrence raises the problem in a circuit arrangement of the type initially set forth of decoupling the auxiliary data bus line which leads to the switch devices of that group that is co-involved in the voltage outage. Whether the appertaining bus amplifier is thereby co-involved in the voltage or not casts in doubt a reliable decoupling in these two possible cases. Such a decoupling is required so that noise influences cannot proceed from the switch devices affected by the voltage outage onto the data bus line which extends from the central control unit not affected by the voltage outage to the switch devices assigned thereto. Such disturbing influences can consist of, for example, an emission of address information or of other data or can consist of an application of disturbing or inhibiting continuous potentials.